The technique which is at present used for packaging monobloc articles having a predominantly prismatic shape with a strip of heat-shrinkable material, or more frequently for packaging groups of individual articles formed for example by containers for products for general use and in particular for foodstuffs and the like in this monolithic prismatic form called hereafter, for simplicity, articles, comprises the use of so-called automatic machines having a discontinuous or continuous movement, whose construction may involve many methods of wrapping the heat-shrinkable material about the individual articles to be packaged.
In accordance with this packaging technique, it is conventional to wrap the article to be packaged in the direction of its movement with the strip of heat-shrinkable material such that this material projects from two opposite faces of this article, the whole then being passed through a tunnel oven in order to cause the said material to adhere by heat-shrinkage to the wrapped faces and to the said two opposite faces of the article by folding of the corresponding material over these latter faces.
Some of these known machines for the packaging of such individual articles which are supplied in a continuous sequence and are disposed in a uniformly spaced manner either discontinuously or continuously, use two strips of this heat-shrinkable material which, at a so-called sealing station, are bought rhythmically from above and from below between two successive articles where they are connected in a transverse manner by sealing and then cut so as to progressively form the closure or seal of a previous article and the junction of the strips for wrapping of the subsequent article. The articles wrapped in this way are then passed into the tunnel oven in order to cause the material to adhere to the wrapped faces by heat-shrinkage and to the two opposite faces of the respective article by folding of the corresponding projecting material over these last two faces (see for example U.S. Pat. No. 3,869,844 and 3,927,507).
Other known machines designed for the packaging of these articles which are caused to move continuously with a uniform spacing involve the use of a single strip of this heat-shrinkable material.
One of these latter known machines involves the supply of this strip parallel to the direction of movement of the articles which are uniformly longitudinally spaced, gradually folding it as it is supplied into a tubular shape with its respective longitudinal edges superimposed on the articles being supplied and joining these superimposed edges by heat sealing. The articles which are wrapped or enveloped in this way in the tubular shape of the strip are then caused to pass, while continuing with their continuous movement, via a first station or a first tunnel oven for a first heat-shrinkage of the material wrapped around the articles, and then, on discharge from this first station, via a second station in which the tubular shaped strip is cut between two successive articles so that material projects from the front and rear faces of two successive articles, and finally via a third station or second tunnel oven which completes the adhesion of the material by heat-shrinkage on the wrapped faces and on the front and rear faces of the article by folding of the corresponding material over these latter faces (see British Pat. No. 1 382 842).
Another of these known machines which uses a single strip for the packaging of articles which are supplied with a continuous movement in a uniformly spaced manner involves, in contrast, supplying this strip from above, in order to extend it above these articles, such that it still projects from two opposite lateral faces and to bring it, by drawing it from the corresponding spool, downwardly in a looped shape until it may be pushed in the feed direction of the articles below the previous article where the looped portion is cut providing two ends or sections of wrapped material, which are respectively the rear end of the previous article and the front end of the article immediately behind. During the continuous movement of the articles, the sections associated with each article are superimposed on one another on the lower face or base of the said article and the articles wrapped in this way are passed in sequence, still in their continuous movement, through a tunnel oven in order to cause the wrapping material to adhere by heat-shrinkage, as is conventional, to the wrapped faces and to the two opposite faces of the article by means of folding of the corresponding material over these latter two faces (see British Pat. No. 1 355 571).
It is also known from the prior art relating to the field of packaging to provide a method of supplying sheets or elements of packaging material progressively cut from a strip wound on a supply spool across the path of the articles to be packaged with a continuous movement so as to fold them into the shape of a horizontal U over the front face and the upper and lower faces which are parallel and adjacent thereto of the article with the end portions of the arms of this U-shape extending beyond the rear face and then to fold these end portions over this latter face where they are joined and sealed in partial superimposition. The means provided for carrying out this packaging method are normally constituted by at least two pairs of opposite belt means having a closed movement designed to grip the longitudinal edges of these sheets in order to bring them across the path of movement of the objects to be packaged (see British Pat. No. 1 037 261 and U.S. Pat. No. 2,424,406), or by only two of these means having a closed movement disposed respectively at the longitudinal edges and designed to entrain them by suction.
The machines which utilise this latter method of folding the packaging material into a U-shape with the final folding and joining of the edges of the sheets by sealing at the rear face of the articles to be packaged require complicated devices both for the final folding and for the sealing as a result of which, in the case of machines for packaging articles with heat-shrinkable material which are already provided with a tunnel oven in order to cause the heat-shrinkable material to adhere to these articles by heat-shrinkage, which material is also therefore heat-sealable, it is preferred to adopt the method described above which involves, as mentioned, folding the heat-shrinkable material firstly around the front, upper, lower, and rear faces of the article and then to fold a trailing end portion with a partial superimposition, over the lower face of the article.
The attempt to eliminate these complicated devices for folding and sealing of portions of these sections on the rear face of the products using the heat source of the tunnel oven to provide for the joining and sealing of the superimposed portions of the sections of the packaging material on the lower face of the articles simultaneously with the operation carried out in the oven to cause the heat-shrinkable packaging material to adhere by heat-shrinkage to the product in order to provide a greater degree of flexibility, i.e. a greater production speed per unit of time, and lower costs for these machines for packaging using the heat-shrinkable material, has not in practice enabled the achievements of these objects as a result of the complexity of the mechanisms used for the folding and superimposition of the above-mentioned end portions of the sections of material on the said lower face of these articles (see for example the above-mentioned GB Pat. No. 1 355 571).